In reply to outtathaway:
Our cat is nocturnal - sleeps most of the day and goes out at night.
We shut her in the kitchen at night, although that's mainly due to her scratching when she wants attention at 4am! She can then come and go via the cat flap. Not a chance of her getting anywhere near our bedroom window.
Occasionally, we find a dead mouse in the kitchen or garden - we generally only see live ones when she drops them in the middle of the lounge while we're still up! I'm getting better at catching them. We've also had 1 live bird, which was more fun to catch and 1 dead chick inside and a couple of dead moles outside.
Friend of mine has trained his cats that the cat flap gets locked at a specific time at night - they know they have to be in by then, or stuck outside until morning.